1. Field of the Invention
This invention relates to a magnetic recording medium, more specifically to a magnetic recording medium suitable as a digital recording medium and having excellent surface characteristics and also excellent electromagnetic transfer characteristics and runnability.
2. Background of the Invention
In a conventional magnetic recording medium, quality has been heightened by making magnetic powder finer or using a multilayer structure in which an upper layer is a magnetic layer and a lower layer is a non-magnetic layer.
However, in the former case, magnetic powder is merely made finer so that sufficient characteristics cannot be obtained. As an example disclosing the latter case, there may be mentioned Japanese Provisional Patent Publication No. 187418/1988. It has been found by the present inventors' investigation that characteristics of non-magnetic powder are not specified therein so that it is impossible to improve dispersibility of magnetic powder or non-magnetic powder in a coating for forming a magnetic layer or a non-magnetic layer and also calenderability in a calender step is lowered, whereby surface characteristics of a magnetic recording medium cannot be in preferred states. Further, they have also found that by using the conventional magnetic recording medium, it is difficult to obtain a magnetic recording medium having excellent electromagnetic transfer characteristics and runnability which are necessary as a digital recording medium.
Also, they have found that when non-magnetic powder containing .alpha.-iron oxide as a main component is merely contained in a coating, dispersibility and standing stability of the coating are low so that when a magnetic recording medium is made to have a multilayer structure, it is difficult to form a sufficiently smooth upper layer coating film, whereby high electromagnetic transfer characteristics cannot be obtained and running durability is worsened.